Y.-K. ZhangÐK. R. Maples · First Synthesis and EPR Evaluation ofPBN-[ tert-13C]
131
To a solution ofthe ketonitrone 1 (2.60 g, ethyl acetate (3:1, v/v). The target nitrone PBN-
15.83 mmol) in anhydrous THF (150 ml) was [tert-13C] was obtained in 14.2% yield (0.4 g). Fur-
added MeMgBr (3.0 M, 10 ml, 30 mmol) at 20 ∞C ther purification by three sublimations at 65 ∞C/1
under argon atmosphere. The mixture was re- torr provided EPR grade sample for the spin trap-
fluxed for 16 h and then cooled to 0 ∞C before ping study. In comparison, the TLC profile of this
NH4Cl-saturated water (8 ml) was slowly added. product was the same as that for unlabeled PBN;
The solvent was rotary evaporated and the residue Rf = 0.12 (silica gel plate, CHCl3); m.p. 71.4 ∞C
1
was dissolved in methylene chloride. Removal of (DSC method). H NMR (270.17 MHz, CDCl3):
the solvent gave a yellowish solid (1.90 g) which δ = 8.28Ð8.25 (m, 2H, o-H ofC 6H5), 7.52 (d, J13C
=
contained at least three components without the 1.5 Hz, 1H, CH=N(O)), 7.40Ð7.36 (m, 3H, p-H,
presence ofthe ketonitrone 1 according to 1H m-H ofC H5), 1.58 (d, J13C = 4.0 Hz, 9H, 3 CH3)
6
1
NMR. The H NMR spectrum also suggested the ppm. 13C NMR (67.94 MHz, CDCl3): δ = 131.10
presence ofthe desired hydroxylamine intermedi-
ate 2 in this mixture. To a solution ofthis mixture
(C1 ofphenyl), 130.16 (C
ofphenyl), 129.88
(broad, CH=N(O)), 128.83 (4C2 and C6 ofphenyl),
in methanol (100 ml) was added a mixed solution 128.48 (C3 and C5 ofphenyl), 70.86 ( 13C isotope,
ofCu(OAc)
monohydrate (0.05 g) and 38% tert-C ofbutyl), 28.40 (d, J13C = 38.4 Hz, CH3).
2
NH4OH (1 ml) in methanol (10 ml). The mixture The assignment of 1H and 13C NMR data was
was stirred under open air until a blue color ap- made with the help ofthe corresponding CH cor-
peared. The solvent was rotary evaporated and the relation NMR spectrum ofthis nitrone product.
obtained residue was chromatographed on silica 13CC10H15NO (178.24): calcd. C 74.68, H 8.48, N
gel eluted with a mixed solvent ofhexanes and
7.86; found C 74.28, H 8.71, N 7.85.
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